Russia announced on Monday that it will supply the Syrian government with modern S-300 missile defence systems following last week’s downing of a Russian plane by Syria, a friendly fire incident that send regional tensions over the war-torn country soaring.

The Russian military aircraft was downed by Syrian government missile defence systems, killing all 15 people on board. Russia laid the blame squarely on Israel, saying that its fighter jets had pushed the Russian plane into the line of Syria’s fire. Shortly before the downing, Israeli strikes had hit targets inside Syria, reportedly preventing an arms shipment going to Iranian-backed Hezbollah group.

Russia launched its campaign in Syria to support President Bashar al-Assad in 2015 and though the involvement turned the tide of war in favour of Syrian government forces, Moscow has since played a careful balancing act, maintaining good ties both with Iran and Israel.

For its part, Israel is wary of Iran’s growing influence in Syria, bringing its arch-enemy closer to its borders.

Last week’s downing has put Russia’s relationship with Israel to a test. President Vladimir Putin struck a reconciliatory note, blaming the downing on a “chain of tragic, fatal circumstances”. But the Russian military came out on Sunday, renewing the accusations against Israel.

Monday’s statement from Russian Defence Minister Sergei Shoigu said Russia will send the newer S-300 missile defence systems to Syria within the next two weeks. Earlier in the war, Russia suspended a supply of S-300, which Israel feared Syria could use against it.

Shoigu said Russia is now going to go ahead with the shipment because “the situation has changed, and it’s not our fault”. The supply of S-300s to Syria will “calm down some hotheads” whose actions “pose a threat to our troops,” he said.

Russia in this case is acting in its interests only, these actions are not directed against third countries

The Kremlin said Russia’s decision was not targeted against anyone and only serves to protect Russian troops in Syria. Spokesman Dmitry Peskov told reporters that recent findings by the Russian military showed an Israeli jet “deliberately” pushed the Russian Il-20 into the line of fire, enabling its downing.

“According to information of our military experts, the reason [behind the downing] were premeditated actions by Israeli pilots which certainly cannot but harm our relations,” Peskov said.

Russia’s stepped-up role in Syria enabled Assad’s forces, which had been losing ground to the armed opposition, to gain the upper hand in the war and reclaim wide swathes of territory held by the rebels.

In recent months, the government recaptured many areas that were controlled by the opposition. And last week, Russia reached a deal with Turkey that averted a Russian-backed offensive against the northwestern province of Idlib, one of the last areas out of government control.

Idlib, controlled by a mix of radical groups and Turkey-backed armed opposition, overlooks the Syrian coast where Russia military and airbases are located, and have reportedly come under rebel fire.

Peskov said the new measures were decided on to boost the security of its troops in Syria.

“Russia in this case is acting in its interests only, these actions are not directed against third countries, but towards defending our own military,” he said.

Shortly after Moscow’s announcement, the Syrian president’s office said Assad received a call from Vladimir Putin and that the two discussed the latest developments, including the Idlib deal and the delivery of S-300s.

According to the statement, Putin reiterated that Russia holds Israel responsible for the downing of the Russian plane. The Russian president also informed Assad of the S-300 delivery, it said.

Assad expressed his condolences for the deaths of the Russian airmen, saying they were “carrying out noble mission, fighting terrorism in Syria”.